The present invention relates to a system and method for delivering filaments, preferably heavy denier filaments, in a dispersed state, to the forming surface of a web-forming means.
Filaments for use in the making of nonwovens can be made by various methods. For example, synthetic polymers can be spun into filaments. These spun filaments are typically drawn-off by a high velocity jet system and blown onto a web-forming surface as is the case in U.S. Pat. No. 3,692,618 to Dorschner. The use of these high velocity jets facilitates high draw-off speeds so that large numbers of filaments can be transported through the system on a continuous basis. A compressed fluid, such as air, is typically employed as the transport medium.
A major problem which occurs when a multiplicity of filaments travel through a high velocity jet system is filament aggregation. "Filament aggregation" is defined as the forming of the filaments into bundles which cause significant uniformity and strength problems when a nonwoven web is formed therefrom.
In an attempt to solve this problem, some formation systems employ complex electrostatic charging apparatus to avoid filament aggregation (see U.S. Pat. No. 3,341,394 to Kinney).
Others try to overcome the filament aggregation problem by accelerating and directing the fibers immediately subsequent to their exit from the high velocity jet stream. An example of the above approach utilizes a phenomenon known as the "Coanda effect". The Coanda effect, which has been known for many years, is exemplified by U.S. Pat. No. 2,052,869 issued to Henri Coanda. Briefly, this phenomenon can be described as the tendency of a fluid, which emerges from an opening, such as slit, under pressure, to attach itself or cling to and follow a surface in the form of an extended lip of the slit, which recedes from the flow access of the fluid as it emerges from the slit. This creates a zone of reduced pressure in the area of the slit so than any entrainable material which is in the area would be entrained and flow with the fluid which has attached itself to the extended lip.
Although the use of a means for imparting a reduced Coanda effect to filaments exiting a high velocity jet system may, in some cases, overcome the aggregation problem associated with light denier filaments, heavy denier filaments, i.e., filaments having a denier of at least 4, which are entrained in a transporting fluid, cannot be effectively dispersed by this reduced Coanda effect. More specifically, when a plurality of heavy denier filaments are transported in a fluid medium at high velocity, the filaments exit the jet system through a slit, are discharged to a region formed between a pair of opposed deflector surfaces, and the entrained filaments enter the dispersion region in close proximity to each other. The reduced Coanda effect is not sufficient to overcome the downward inertia of the above heavy denier filaments. Therefore, substantial deflection of the filaments toward the deflection surfaces, at a corresponding substantial dispersion of the filaments, cannot be accomplished. The filaments thus essentially remain in close proximity to each other as they are deposited on the forming wire, which results in the previously described formation problems.
In U.S. Pat. No. 3,485,428 to Jackson, a horizontally disposed, sequentially directed low pressure fluid is intermittently supplied to a diverging chamber through which strands of yarn exit. Thus, the fluid which emanates from the two diametrically opposed jets impinges the high velocity stream of filaments and exerts a "pushing" force or pressure on the filaments in a reciprocating manner. The above approach does not, however, cause the heavy denier fibers previously described to be dispersed in a manner required for effective, nonwoven product formation. Instead, the entire bundle of filaments, which are in close proximity to each other, are moved from side to side as they are impinged by the intermittently directed low pressure air flow without causing effective dispersion of the filaments with respect to each other.